1. Field of the Invention
This invention relates to biopharmaceutical material cryogenic preservation methods and apparatus, and more particularly to a biopharmaceutical material cryogenic preservation system and method which maintains a controlled dendritic freezing front velocity.
2. Description of Related Art
Cryopreservation of biopharmaceutical materials is important in the manufacturing, use, storage and sale of such materials. For example, biopharmaceutical materials are often cryopreserved by freezing between processing steps and during storage. Similarly, in certain cases, biopharmaceutical materials are frozen and thawed as part of the development process to enhance their quality or to simplify the development process.
When utilizing cryopreservation, the overall quality, and in particular pharmaceutical activity, of the pharmaceutical materials is desirably preserved, without substantial degradation of the biopharmaceutical materials.
Currently, in some aspects, cryopreservation of biopharmaceutical materials involves placing a container comprising the biopharmaceutical materials in a cabinet or chest freezer and allowing the biopharmaceutical materials to freeze. In current cryopreservation techniques, a container enclosing biopharmaceutical materials is placed on a solid or wire-frame shelf in the cabinet or chest freezer. The biopharmaceutical materials are left to freeze until they are solid, in an uncontrolled fashion.
Significant losses in biopharmaceutical material activity have been noted using such current techniques. For example, observers have noted that stability and conformation of biopharmaceutical materials can be affected by low temperature alone, without any significant changes in variables such as solute concentration or pH.
Further, it has been noted that conventional cryopreservation methods can lead to cryoconcentration, or the redistribution of solutes from the frozen volume to the unfrozen cavity where their concentration may significantly increase. The result of cryoconcentration can include the crystallization of buffer components leading to a pH change that can affect stability, folding, or even create cleavage of the biopharmaceutical material. Cryoconcentration in conjunction with low temperature effects may cause a decrease in solubility of the biopharmaceutical material, with resulting precipitation. Product aggregation (i.e. increase in molecular weight) has also been observed.
Additionally, damage to the containers has been noted using conventional cryopreservation techniques. Container damage may be caused by freezing stress due to volumetric expansion of aqueous biopharmaceutical materials during freezing. Rupture or damage to the integrity of the container is undesirable, as it can compromise sterility or lead to biopharmaceutical material contamination or leakage or loss of the biopharmaceutical material.
Another problem faced by those of skill in the art is that currently available process methods and apparatus designs intended for cryopreservation of biopharmaceutical materials generally do not exhibit good linear scalability. In biopharmaceutical manufacturing, there is a constant need for simple, efficient and predictable scale-up. Methods developed at research and pilot stages should be directly scalable to the production scale without compromising biopharmaceutical material quality (e.g. biological activity of the biopharmaceutical material) or process productivity. The predictability of process behavior based on information developed on a small scale is often referred to as linear scalability.
In scaling up a cryopreservation process, discrete containers such as bottles, carboys, tanks, or similar single containers are available in different sizes. In virtually all cases, the rate of completely freezing the biopharmaceutical materials in each vessel is related to the largest distance from the cooling surface. Consequently, longer times are required to freeze the contents of larger containers if the same cooling surface temperature is maintained. Such longer times are undersirable because this results in lower process throughputs. Additionally, increases in the freezing volume may have an unpredictable impact on biopharmaceutical material activities in certain cases.
Various strategies have been adopted to mitigate this scale up problem. To freeze large quantities, one could for example use multiple smaller containers. However, adjacent placement of multiple containers in a freezer creates thermal gradients from container to container. The freezing rate and product quality depend on the actual freezer load, spacing between the containers, and air movement in the freezer. The result is different thermal history for the contents of individual containers. For a large batch, it is also time consuming and counter-productive to divide the lot into a large number of subunits. Product loss is likely to be important as it is, to some extent, proportional to the container surface and to the number of containers.
Accordingly, there is a need for apparatus and methods for cryopreservation of biopharmaceutical materials that solve the deficiencies noted above.
In an aspect, the invention relates to a biopharmaceutical material cryopreservation system comprising a flexible sterile container comprising a biocompatible polymeric material, and the flexible sterile container containing biopharmaceuticals materials, and; a freezing system removably coupled to the flexible sterile container via a tapered slot and the freezing system thermally coupled to the biopharmaceutical materials via the flexible sterile container and the tapered slot; wherein the freezing system comprises a feedback loop constructed to control a dendritic freezing front velocity, within the biopharmaceutical materials, in a range from approximately 5 millimeters per hour to approximately 250 millimeters per hour based on feedback information from the temperature sensor.
In another aspect, the invention relates to a method for cryopreservation of biopharmaceutical materials, comprising providing a flexible sterile container comprising a biocompatible polymeric material, and the flexible sterile container containing biopharmaceuticals materials thermally coupling a freezing system to the biopharmaceutical materials via the flexible sterile container, and the freezing system comprising (i) a temperature sensor that monitors a temperature of the iopharmaceutical materials, and (ii) a feedback loop constructed to control a dendritic freezing front velocity; and controlling the dendritic freezing front velocity, within the biopharmaceutical materials, in a range from approximately 5 millimeters per hour to approximately 250 millimeters per hour based on feedback information from the temperature sensor.
In yet another aspect, the invention relates to a biopharmaceutical material cryopreservation system, comprising flexible sterile container means for counting biopharmaceutical products, and the flexible sterile container means comprising a biocompatible polymeric material, and the flexible sterile container containing biopharmaceuticals materials, and; freezing means for freezing the biopharmaceutical materials, and the freezing means thermally coupled to the biopharmaceutical materials via the flexible sterile container, and the freezing means comprising a temperature sensor that monitors a temperature of the biopharmaceutical materials wherein the freezing means comprises a feedback loop constructed to control a dendritic freezing front velocity, within the biopharmaceutical materials, in a range from approximately 5 millimeters per hour to approximately 250 millimeters per hour based on feedback information from the temperature sensor.
In still another aspect, the invention relates to a method of linearly scaling a process for cryopreserving a biopharmaceutical material comprising providing the biopharmaceutical material cryopreservation system of claim 1, wherein the biopharmaceutical material cryopreservation system possesses a first volume defined by a slab length, height, taper angle, and a first z dimension; determining a second volume; determining a second z dimension based on the values of the second volume, the slab length, the height, and the taper angle; and providing the biopharmaceutical material cryopreservation system, wherein the biopharmaceutical material cryopreservation system possesses the second volume defined by the slab length, the height, the taper angle, and the second z dimension.